A program to be carried out on transparent liquid-phase miscibility gap materials was developed for the purpose of acquiring additional insight into the separation process occurring in these systems. The transparency feature allows the reaction to be viewed directly through light scattering and holographic methods

Bhat, B. N.

Gelles, S. H.

Laub, R. J.

English

NASA Technical Reports Server

PHASE SEPARATION IN TRANSPARENT LIQUID-LIQUID MISCIBILITY GAP SYSTEMS
by
S. H. Gelles, B. N. Bhat^' and R. J. Laub^
INTRODUCTION
The field of processing materials in space has provided a renewed
incentive to study materials systems containing a liquid phase miscibility gap,
i.e., a field in the phase diagram representing the equilibrium between two
liquid phases. These studies have concentrated on understanding the development
of both the macro- and microstructures of these materials during thermal process-
ing and have also taken advantage of the low-gravity environment afforded
by sounding rockets and orbiting spacecraft to minimize the effects of buoyancy
and fluid flow. The programs have generally concentrated on opaque metallic
systems and have been primarily concerned with the separation process wherein
a single phase liquid transforms into two liquid phases and with the accompanying
coalescence processes. Since solidification can affect the macro- and micror
structures, this transformation has been studied as well.
As will be delineated in what follows, the studies of the metallic
systems at low-g have led to unexpected results, and have prompted the analysis
of mechanisms which might have disturbed the transformation and led to the
unusual results observed. These disturbing effects are generally difficult to
analyze even if they occur alone. They are all the more complicated when more
than one mechanism is involved. Moreover, other processes that as yet have
not been conceptualized may also occur. It is with these factors in mind that
we have outlined a program to be carried out on transparent liquid-phase
miscibility gap materials for the purpose of acquiring additional insight into
(a)S. H. Gelles Associates, Columbus, OH 43204
Department of Chemistry, Ohio State University, Columbus, OH 43201
https://ntrs.nasa.gov/search.jsp?R=19820024183 2020-03-21T07:47:19+00:00Z
the separation process occurring in these systems. The transparency feature allows
the reaction to be viewed directly through light scattering and holographic
methods.
BACKGROUND
A number of opaque miscibility gap metallic systems have been made
(1-8)
the subject of ground base and flight studies. We have been studying
(1 2)
aluminum-indium alloys ' in terrestrial and SPAR rocket experiments. In
a typical experiment, an alloy of composition within the extremes of the
miscibility gap is heated into the single phase liquid field above the
(29)
miscibility gap (See Figure 1) ' held for a time sufficient to homogenize
the alloy and then cooled through the gap at a controlled cooling rate. It
was expected that the structure resulting from conducting this heat treat-
ment at low-g would consist of a uniform precipitate contained within a
host phase. In the aluminum-rich end of the miscibility gap the dispersed
phase would be rich in indium while indium-rich alloys would produce aluminum-
rich precipitates in an indium-rich phase. The Al-In alloys processed at
1-g would consist of a layered structure with the indium-rich phase at the
bottom and the aluminum-rich phase floating on the top.
Samples of various compositions of aluminum-indium alloys have been
processed on both the SPAR II and SPAR V sounding rocket flights. An example
of the results obtained is shown in Figure 2 where the macrostructures of an
Al-40 and -70 wt. Pet. In alloy processed on SPAR II are compared with their
ground base counterparts. The ground base samples possess the expected
layered structures but those processed in space did not produce the anticipated
uniform dispersions. Instead, as may be seen in Figure 2a, the structure
900
800
700
600
o
o 500
CDCL
400
300
200
1 00
Al
0
Al
AI(s)+Ln
156 C
10 20 30 40 50 60 70
Weight Percent Indium
FIGURE 1. THE ALUMINUM-INDIUM EQUILIBRIUM DIAGRAM
80
(2,9)
90 100
In
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Si
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ORIGINAL PAGE IS
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Flight
(a)
Al-70 wt. % In
Al-40 wt. % In
Ground Base
(b)
FIGURE 2. MACROSTRUCTURE OF SPAR II Al-In ALLOYS
AND THEIR GROUND-BASE COUNTERPARTS
consists of a massively separated aluminum-rich core surrounded by indium-
rich material. Observations similar to these have been made in other metallic
miscibility gap systems processed at low-g (See for example References 3-5).
Various mechanisms generally involving fluid flow have been proposed
to explain the structures of the miscibility gap alloys processed in space.
A listing of these mechanisms is presented in Table 1. Some of them have been
considered in detail from a theoretical standpoint while others have as yet not
been analyzed. For example, detailed calculations have been made on the
residual fluid motion present after spin-up and despin in the SPAR rocket
experiments with the conclusion that this potential source of fluid motion did
not significantly contribute to the development of the observed structures;
Similarly, inhomogeneities in the starting Al-In alloys have been ruled out
as being contributory after extensive measurements of liquid phase diffusion
had been made and after long homogenization times had been applied to the
experimental procedure with rib discernable difference in results.
Evidence has been obtained that surface tension driven fluid motion
has influenced the structure of the Al-In alloys processed in SPAR II and SPAR
V. In support of this model, wave-like structures have been observed at the
liquid- liquid interfaces and in addition evidence of droplet migration driven
(2)by surface tension forces has been presented as shown in Figure 3 . The
alloy illustrated in this figure is an Al-90 wt. pet. In alloy processed
aboard SPAR V. The macrostructure consists" of two massive aluminum-rich regions
surrounded by indium-rich material. Adjacent to the larger aluminum-rich
region is an annular area that consists of agglomerating aluminum- rich
spheres (See Figure 3b). Further away from the aluminum-rich metal, there
ORIGINAL
OF POOR QUALITY
TABLE 1. POSSIBLE MECHANISMS FOR MASSIVE PHASE SEPARATION
Residual Fluid Motion
Surface Tension Drive Flow (Marangoni Effect)
Conventional Convection
Capillarity (Spreading)
Transformation Segregation
Transformation Volume Changes
Nonuniform Starting Composition
ORIGINAL PAGE
BLACK AND WHITE PHOTOGRAPH
10x
FIGURE 3. STRUCTURE 0* Al-90 WT. PCT. In
(a) Macro View of Longitudinal
structure of Region A in (a)
Region B in (a). of
lOOx
in an area that is relatively free of the aluminum-rich spheres (Figure
3 c.) . These structural observations can be explained by a model consisting of
the aluminum-rich spheres migrating to the warmer regions of the molten alloy
during cooling through the miscibility gap. Quantitative support for this
(2)
model has also been obtained.
It is rather difficult to sort out the various phenomena that are
contributing to.the structural evolution of the liquid-phase miscibility
materials. This is especially difficult in opaque systems where generally
only the final structure is available for analysis of the mechanisms which
might have contributed to its formation. Studies in transparent analogue
systems would offer two distinct benefits. First of all, they would allow
direct observations of the fluids during transformation and secondly, they
would provide systems with a wider range of physical properties so that the
importance of various physical parameters can be assessed in terms of phase
separation kinetics and emulsion stability. In the following, section we outline
an experimental program dealing with transparent liquid phase miscibility
gap systems which would supplement the present research activities on the
metallic systems.
SUGGESTED RESEARCH PROGRAM ON LIQUID PHASE MISCIBILITY GAP SYSTEMS
A study of transparent liquid phase miscibility gap systems would
have as its objectives: .
1. To view phase-separation in situ in an attempt to determine
the mechanism of massive separation previously seen in metallic
systems.
ORiGiNAL PAGE ^
OF POOR QUALfTY
10
2. To determine the effect of material properties on the kinetics
of phase separation, on the occurrence of various fluid flow
mechanisms and on emulsion stability.
To accomplish these objectives, we are suggesting the following
program which can be organized into the following phases.
Phase 1. System Selection .
Phase 2. Ground Base Experiments
Phase 3. Flight Experiments
System Selection
This part of the program would be devoted to the very important
task of selecting the proper systems for study. In the selection process
the most important parameters are the physical properties such as the surface
energies and interfacial energies between the two coexisting liquids and
their variation with composition and temperature. In addition, fluid flow
properties such as viscosities are of importance. Aside from these basic
physical properties, it is important to select systems that are convenient
to work with, i.e. that have convenient consolute temperatures, miscibility
gap widths and heights and which will not create excessive handling problems,
due to extreme toxicity,- for example, or to a requirement for ultra-purifica-
tion. Examples of three types of transparent liquid phase misciblity gap
systems are shown in Figure A. Figure 4a shows the more common type with
an upper critical temperature, whereas Figure 4b shows one with a lower
critical temperature. Figure 4c has both upper and lower critical temperatures.
Ground Base Experiments .
It is envisioned that the ground base research would be in three areas.
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1. System property evaluation.
2. Phase separation kinetics and emulsion stability.
3. Fluid flow mechanisms.
System Property Evaluation :
In this portion of the program, the literature dealing with the physical
parameters listed in Table 2 would be reviewed for the selected systems and the
reliability of pertinent published data would be assessed. In those cases where
the data are missing or unreliable, supplementary measurements would be made.
Phase Separation Kinetics
Phase separation kinetics and emulsion stability of various trans-
parent systems having a wide range of material properties would be evaluated
by means of light scattering and holographic techniques. The effect of compo-
sition within the miscibility gap would be determined in both isothermal and
controlled cooling rate experiments. In the isothermal experiments, a chemical
mixture making up the transparent system would be cooled or heated from a single
phase liquid field into the two phase liquid field where it would be held
and monitored as a function of time by such techniques as light scattering..
In the cooling rate experiments, the samples would be cooled at controlled
rates through the miscibility gap again while monitoring the particle size
distribution as a function of time. The results of these experiments would
be compared to theoretical models dealing with nucleation, droplet collisions,
coalescense and emulsion stability.
Fluid-Flow Mechanisms
Transparency in the systems of interest will provide the opportunity; to
carry out experiments on the mechanisms of fluid flow which affect the stability
and structure of liquid phase miscibility gap systems. Such mechanisms
include droplet migration under the driving force of surface tension, thermo-
13
TABLE 2. PHYSICAL PROPERTIES OF INTEREST IN STUDIES ON.
TRANSPARENT MISCIBILITY GAP MATERIALS
Phase Equilibra
Viscosities
Interfacial Energies
Thermal Properties
Diffusional Characteristics
Transformation Volume Changes
ORSG'NAL PAGE IS
OF POOR QUALITY
capillary and solutalcapillary convection, spreading, fluid motion due to volume
changes associated with transformations and fluid motion due to coalescense
mechanisms. The experimental approach would be supplemented with theoretical
modeling.
LOW GRAVITY EXPERIMENTS .
Experiments dealing with transparent liquid phase miscibility gap
systems at low gravity will be designed with the objective of determining
the effect of gravity on the separation kinetics, emulsion stability and fluid
flow phenomena associated with the phase separation. The Fluids Experiment
System (FES) now being designed would appear to be a suitable apparatus in
which to carry out these experiments. Specific experiments dealing with the
pertinent mechanisms of fluid flow would probably develop from the ground
base studies.
The rationale for conducting these studies at low gravity is to reduce
the complications associated with buoyancy effects, conventional convection
and their associated contributions to droplet collisions.
ANTICIPATED BENEFITS
The extension of the research on liquid phase miscibility gap systems
into studies on transparent systems should provide insight into the mechanisms
causing massive separation in metallic miscibility gap alloys. The research
should also provide a better understanding of the effect of material para-
meters on phase separation kinetics, droplet size distribution, and emulsion
stability. Since the experiments on transparent systems would allow measure- :
ments of the separation process to be made while the reaction is occurring
these systems would also be ideal for studying spinodal decomposition.
15
The research would also provide insight into the fluid flow mechanisms which
are active in these systems and which may be accentuated in an acceleration-
free environment. With the attaining of an understanding of the material
parameters of importance in the phase separation, it will be far easier to
select systems of potential technical importance.
16
REFERENCES
1. S. H. Gelles and A. J. Markworth, "Microgravity Studies in the Liquid
Phase Immiscible System: Aluminum-Indium," AIAA Journal, 16 (1978) 431.
2. S. H. Gelles and A. J. Markworth, "Final Post-Flight Report on SPAR V
Experiment 74-30, Agglomeration in Immiscible Liquids," Final Report
to NASA-MSFC on Contract NAS8-31542, October, 1979.
3. L. L. Lacy and C. Y. Ang, "Monotectic arid Syntectic Alloys Experiment
MA-044," Apollo-Soyuz Test Project Summary Science Report, Vol. 1, NASA
SP-412, 1977.
4. H. U. Walter, "Stability of Multi-Component Mixtures Under Microgravity
Conditions," Presented at the Third European Symposium on Materials Science
in Space, Grenoble, France, April 24-27, 1979.
5. T. Carlberg and H. Fredriksson, "The Influence of Microgravity on the
Structure of Bismuth-Zinc Immiscible Alloys," Presented at the Third
European Symposium on Materials Sciences in Space, Grenoble, France,
April 24-27, 1979.
6. J. L. Reger, "Experimental Development of Processes to Produce Homogenized
Alloys of Immiscible Materials," Final Report, III, Prepared Under Contract
NASA-27805, to NASA-MSFC, TRW Report 18677-6019-RU-OO, Jan., 1973.
7. C. Potard, "Directional Solidification of Aluminum-Indium Alloys at Micro- .
Gravity: Results of Basic Preparatory Investigations," Paper Presented
at the 17th Aerospaces Meeting, AIAA, New Orleans, La., Jan. 15-3)7, 1979.
8. H. Ahlborn and K. Lohberg, "Aluminum-Indium Experiment SOLUOG - a Sounding
Rocket Experiment on Immiscible Alloys," Paper 790172 Presented at the 17th
Aerospace Sciences Meeting, AIAA New Orleans, La., Jan. 15-17, 1979.
9. B. Predel, "Beitrag zur Konstitution und Thermodynamik von Entmischungssystemen,"
Zeitschrift fur Metallkunde, 56 (1965) 791.
17


Phase separation in transparent liquid-liquid miscibility gap systems

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